Báo cáo y học: "Outbreak of chickenpox in a refugee camp of northern Thailan" pot

SHOR T REPOR T Open Access
Outbreak of chickenpox in a refugee camp of
northern Thailand
Yusuke Shimakawa
1,2
, Olivier Camélique
2
, Koya Ariyoshi
1*
Abstract
Although chickenpox is a generally mild, self-limited illness of children, it can cause fatal disease in adults. Accumu-
lating reports from tropical countries showed a high prevalence of seronegativity among the adults, implying that
varicella diseases could become a heavy burden in tropical countries. However, in the situation of humanitarian
emergencies in tropical areas, chickenpox has larg ely been ignored as a serious communicable disease, due to lack
of data regarding varicella mortality and hospital admissions in such a context. This is the first report describing an
outbreak of chickenpox in a refugee camp of tropical region. In 2008, we experienced a varicella outbreak in ethnic
Lao Hmong refugee camp in Phetchabun Province, northern Thailand. The attack rate was 4.0% (309/7,815) and
this caused 3 hospitalizations including one who developed severe varicella pneumonia with respiratory failure. All
hospitalizations were exclusively seen in adults, and the proportion of patients ≥15 years old was 13.6% (42/309).
Because less exposure to varicella-zoster virus due to low population density has previously been suggested to be
one of the reasons behind higher prevalence of susceptible adults in tropics, the influx of displaced people from
rural areas to a densely populated asylum might result in many severe adult cases once a varicella outbreak occurs.
Control interventions such as vaccination should be considered even in refugee camp, if the confluence of the risk
factors present in this situation.
Findings
Although varicella occurs universally, its epidemiology is
remar kably different in tropical and temperate areas [1].
In temperate countries, more than 90% of people are
infected before adolescence [2], whereas in tropical
regions varicella tends to occur at a later age causing
many adult cases, suggested by the report s, demonstrat-

ing a high prevalence of varicella seronegativity among
adolescents and adults [1,3-6].
Adult varicella patients are known to develop severe
disease with a higher rate of complications than children
[7], and pregnant women with primary varicella-zoster
virus (VZV) infection are at risk of transmitting the infec-
tion to their unborn child causing congenital varicella
syndrome. Although these factors indicate that the health
burden attributable to varicella disease in tropical settings
is much heavier than previously assumed [1], data on
mortality and hospital admissions from the tropics are
sparse [2]. Here, we report the first description of a vari-
cella outbreak in a refugee camp in a tropical region.
The international medical humanitarian organization
Médecins Sans Frontières (MSF) began providing medi-
cal and logistic aid to ethnic Lao Hmong refugees in
Phetchabun Province, northern Thailand in July 2005,
and opened the sol e outpatient clinic in this camp. Peo-
ple were confined to a guarded, barbed-wire enclosed
camp controlled by the T hai military, and one house-
hold unit consisting of an average of 5 to 6 persons
living in a small barracks. Barracks are clustered close
together in a small area of 20 hectares. The total regis-
tered population in February 2008 was 7,815, including
1,930 children <5 years old. Although the majority
recently fled from Laos, an estimated 1,000 Hmong
were from a former refugee camp in central Thailand
[8]. On the basis of MSF data in 2007, the average
monthly crude mortality rate at the camp was 1.89 per
10,000 persons. Although there is no information on the

overall prevalence of HIV infection, no cases were
detected since the introduction of routine voluntary
testing for pregnant women. As there was no inpatient
facility inside the camp, seriously ill individuals were
referred to the district hospital.
* Correspondence:
1
gCOE program, Institute of Tropical Medicine (Nekken), Nagasaki University,
1-12-4, Sakamoto, Nagasaki-shi, 852-8523, Japan
Shimakawa et al. Conflict and Health 2010, 4:4
/>© 2010 Shimakawa et al; licensee BioMed Central Ltd. This is an Open Access article distributed u nder the terms of the Creative
Commons Attributio n License ( which permits unrestricted use, distribution , and
reproduction in any medium, provided the original work i s properly cited.
DuringthefifthweekofJanuary2008,theincidence
of varicella started to increase in the camp. Between
January 28 and May 3, there were 309 cases of varicella
(Figure 1), which was defined as an a cute onset of
diffuse maculo-papulovesicular rash without other
apparent causes [9]. Overall community attack rate was
4.0% (309/7,815): 8.5% (164/1,930) and 2.5% (145/5,885)
for those aged <5 years and ≥5 years, respectively. Med-
ian age was 4 year s, ranging from 3 months to 53 years,
and 42 (13.6%) patients were ≥15 years old. Among 165
(53.4%) female patients, five were pregnant. No severe
complications occurred among the patients <15 years
old, except 2 children with cellulitis who were treated
on an outpatient basis. However, among the 42 patients
≥15 years old, 3 (7.1%) were admitted to the district
hospital. They were all previously healthy: a 30-year-old
man with severe dehydration, a 21-year-old pregnant

woman with varicella pneumonia, and a 53-year-old
man with varicella pneumonia followed by respiratory
failure which required mechanical ventilation and
admission to ICU. They were discharged without seque-
lae. All pregnant women who contracted varicella were
followed-up until delivery, with no documented compli-
cations including birth defects. There were no particular
clusters of barracks at higher risk of infection, and the
isolation of patients as control measure was not feasible
in this context. Only symptomatic treatment and anti-
biotics were available for case management.
This outbreak highlights two important findings.
While the majority of patients were children, we found
the proportion of patients ≥15 years old to total number
of patients was higher than in tempera te countries: 3%
in the United States during the prevaccine era [7], 8% in
France [10] and <1% in Japan [11]. Furthe rmore, all the
hospitalizations were exclusively seen in those aged ≥15
years and the rate of hospitalizations per 1,000 cases
was 9.7 (95% CI, 2.0-28.4). This was also higher than
those reported from temperate countries: 1.2 in the Uni-
ted States [7] and 4.7 in France [10].
The exact mechanism of such an epidemiological
variation in the tropics is largely unknown. Nevertheless,
proposed explanations included interference with VZV
transmi ssion from high temperature [3,5], less opportu-
nity to contract VZV during childhood in rural areas
[4,5], competition with other viral pathogens [12], and
cross-antigenicity between VZV and herpes simplex
virus [13]. As most of Hmong in this camp recently fled

from the rural areas of Laos, one might speculate that
many reached adulthood without coming into contact
with VZV, and contracted varicella subsequently to their
settlement in the camp of high population density.
Although there were no deaths, two adult patients with
varicella pneumonia were a substantial health burden
for this camp. These indicate that in tropical regions,
the influx of displaced people from rural areas to a den-
sely populated asylum might result in many severe adult
cases once a varicella outbreak occurs. Control interven-
tions such as vaccination should be considered even in
refugee camp, if the confluence of the risk factors
present in this situation.
Acknowledgements
First, we authors would like to thank Médecins Sans Frontières and
Epicentre, Paris for authorization to use the data and technical advice. We
also thank Riko Nakamura, Tomoko Abe, Naho Tsuchiya, Motoi Suzuki,
Masahiro Hashizume, and Sumihisa Honda, who contributed to improve the
manuscript and Itsuki Murakami for her great communication support.
Author details
1
gCOE program, Institute of Tropical Medicine (Nekken), Nagasaki University,
1-12-4, Sakamoto, Nagasaki-shi, 852-8523, Japan.
2
Médecins Sans Frontières,
8 rue Saint Sabin, 75011, Paris, France.
Figure 1 Epidemic curve for varicella outbreak. Number of varicella cases by date of diagnosis in the Lao Hmong refugee camp, from Jan 28
to May 3, 2008.
Shimakawa et al. Conflict and Health 2010, 4:4
/>Page 2 of 3

Authors’ contributions
YS was a field doctor at this refugee camp, and collected all of the data as
part of his routine work. OC was a medical coordinator of this camp, and
supervised work of YS. KA participated in the interpretation of the results.
OC and KA participated in the critical revision of the manuscript. All authors
read and approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 24 January 2010 Accepted: 22 February 2010
Published: 22 February 2010
References
1. Lee BW: Review of varicella zoster seroepidemiology in India and
Southeast Asia. Trop Med Int Health 1998, 3 :886-90.
2. Heininger U, Seward JF: Varicella. Lancet 2006, 368:1365-76.
3. Garnett GP, Cox MJ, Bundy DAP, Didier JM, Catharine JST: The age of
infection with varicella-zoster virus in St Lucia, West Indies. Epidemiol
Infect 1993, 110:361-72.
4. Mandal BK, Mukherjee PP, Murphy C, Mukherjee R, Naik T: Adult
susceptibility to varicella in the tropics is a rural phenomenon due to
the lack of previous exposure. J Infect Dis 1998, 178(Suppl 1):52-4.
5. Lolekha S, Tanthiphabha W, Sornchai P, Kosuwan P, Sutra S, Warachit B,
Chup-upprakarn S, Hutagalung Y, Weil J, Bock HL: Effect of climatic factors
and population density on varicella zoster virus epidemiology within a
tropical country. Am J Trop Med Hyg 2001, 64:131-6.
6. Nysse LJ, Pinsky NA, Bratberg JP, Babar-Weber AY, Samuel TT, Krych EH,
Ziegler CAW, Jimale MA, Vierkant RA, Jacobson RM, Poland GA:
Seroprevalence of antibody to varicella among Somali refugees. Mayo
Clin Proc 2007, 82:175-80.
7. Guess HA, Broughton DD, Melton LJ III, Kurland LT: Population-based
studies of varicella complications. Pediatrics 1986, 78(4 Pt 2):723-7.

8. Doctors Without Borders/Médecins Sans Frontières (MSF): Fearing a forced
return. The situation of the Lao Hmong refugees in Petchabun, Thailand.
[ />Hmong_Briefing.pdf].
9. Centers for Disease Control and Prevention (CDC): Case definitions for
infectious conditions under public health surveillance. Varicella case
definition 1999. [ />varicella_current.htm].
10. Boëlle PY, Hanslik T: Varicella in non-immune persons: incidence,
hospitalization and mortality rates. Epidemiol Infect 2002, 129:599-606.
11. Infectious Disease Surveillance Center: Chickenpox 1982-2004. Infectious
Agents Surveillance Report 2004, 25:318-20. [ />tpc298.html].
12. Bang FB: Epidemiological interference. Int J Epidemiol 1975, 4:337-42.
13. Edson CM, Hosler BA, Respess RA, Waters DJ, Thorley-Lawson DA: Cross-
reactivity between herpes simplex virus glycoprotein B and a 63,000-
dalton varicella-zoster virus envelope glycoprotein. J Virol 1985, 56:333-6.
doi:10.1186/1752-1505-4-4
Cite this article as: Shimakawa et al.: Outbreak of chickenpox in a
refugee camp of northern Thailand. Conflict and Health 2010 4:4.
Submit your next manuscript to BioMed Central
and take full advantage of:
• Convenient online submission
• Thorough peer review
• No space constraints or color figure charges
• Immediate publication on acceptance
• Inclusion in PubMed, CAS, Scopus and Google Scholar
• Research which is freely available for redistribution
Submit your manuscript at
www.biomedcentral.com/submit
Shimakawa et al. Conflict and Health 2010, 4:4
/>Page 3 of 3